Machines for moving materials such as earth and stones, including excavators and the like, and other machines used in public works and mining, are used for pulling up, moving and loading earth, stones and the like. These machines, which can be presented under a variety of configurations, are usually provided with one or more buckets attached to a mechanical arm. The bucket is provided with a blade or beveled lip on a front edge intended to strike and penetrate the mass of earth and stones. To prevent excessive wear of the blade and to aid in penetrating the earth, it is common to assemble wear elements or teeth associated to the blade and projecting in front of same. However, said teeth are also subjected to wear and breakages, therefore they must be replaced often, and on the other hand, depending on the work for which the machine is intended, it may be desirable to change the type or the shape of the teeth. In order to facilitate said replacement, tooth holders are used, which are secured to the blade of the bucket in a more or less permanent manner, and the teeth are releasably assembled in the tooth holder by means of pins. Said pins usually traverse apertures of the tooth and a passage traversing the tooth holder for the purpose of securing the tooth to the tooth holder.
To prevent the pin from coming out of its assembly position, a retaining device is used, which device maintains the pin in said assembly position. The retaining device normally includes elastic elements having the function of exerting pressure on the retainer so that the latter remains in its assembly position. In working conditions, the system receives forces and blows in all directions, making the system move and reacting in an unwanted manner, causing internal wear and shifting the pin. The pin can then come out of the tooth holder, the pin and the tooth possibly being lost. The loss of a tooth and/or pin can be very important depending on the work site thereof, given that they can cause other machines to break down, such as crushers, working in the same production site as the machine using the teeth, such as for example mines or quarries.
Patent application number WO-2005095720-A1 describes a device for the detachable fastening of two mechanical pieces, comprising a pin which removably blocks a first piece with respect to a second piece, a retaining element associated to the pin and an elastically loaded tensor element, collaborating to prevent the pin from coming out of its blocking position; in this system it further comprises at least two inclined planes the general shape of which is that of a projection oriented in the axial direction of the pin, such that upon rotating the pin, the retaining element travels said inclined planes and the pin moves between two positions, the blocking position and the unblocking position or the introduction position of the pin, against the axial force exerted by said tensor element in the direction of the axis of the pin.
In combination with the elastic load of the tensor element and the retaining element, the two inclined planes make it very difficult for the pin, with said retaining element, to come out of its blocking position. During its working operation, the pin can receive both longitudinal and transverse stressing, but it will be difficult for it to receive stresses causing a rotation thereof, such that the retainer of the pin cannot rotate from its blocking position upon introducing the pin in the cavity formed by the male piece and the female piece.
In the blocking position, the pin is completely introduced in the channel or housing forming the apertures of the tooth and of the tooth holder, the pin preferably not being a through pin, i.e., it does not traverse the two sides of the tooth, only one of them for the introduction thereof. When the tooth is worn or the design thereof has to be changed, it will be necessary to first remove the pin. In this type of system, the stresses for disassembly are greater than those for the assembly, because in addition to the difficulties characteristic of the design and construction, the disassembly is affected because during the work, the pin and the retaining element can become deformed in addition to earth being introduced in the housing of the pin, making the extraction thereof difficult.
The movements of the fastening device under extreme working conditions are unpredictable and often uncontrollable. After several hours of working in a number of field tests, it was found that the pin had experienced movement in an unwanted direction; specifically it had shifted with respect to its working or blocking position, towards the end opposite that for introducing the pin in the tooth. In other words, as the end of the pin introduced in the tooth holder had shifted, it tends to come out through the aperture of the tooth opposite the introduction aperture for introducing it. In the blocking position, the retainer of the pin is located between an inner wall of the tooth and a wall of the tensor, and due to the stress in work, the pin moves in the only direction that is not limited, which is towards the tensor due to the fact that the material thereof is not as hard as that of the tooth.
If the pin shifts from its blocking position such that the end of the pin introduced in the tooth holder projects through the aperture of the tooth opposite the introduction aperture for introducing it, the pin thus being exposed to unwanted wear. Furthermore, upon receiving the constant pressure exerted by the retainer of the pin, the tensor is damaged, losing its technical characteristics.
In the rotation for assembling the pin in application number WO-2005095720-A1, the internal rotation of the retainer is not visibly controllable from the outside, therefore the retainer rotates until it has travelled along the entire surface of the tensor, coming out of contact with the tensor and being housed between the tensor and a wall of the cavity of the tensor existing in the tooth holder.
The unwanted housing of the retainer of the pin between the tensor and a wall of the cavity of the tensor, in addition to a possible constant pressure of the retainer on the tensor, make it difficult to extract the pin from the tooth-tooth holder system.